Composite airfoil with integral platform

ABSTRACT

A method of forming an airfoil with an integrated platform includes: a) providing an airfoil core; b) wrapping a first overwrap ply around the airfoil core; c) darting a first end of the first overwrap ply to allow the overwrap ply to extend perpendicular to the airfoil core to form a first platform; d) filling the darted parts filler plies; e) wrapping a second overwrap ply around the first overwrap ply; f) darting a first end of the second overwrap ply to allow the second overwrap ply to extend adjacent to the first overwrap ply to form the first platform; g) filling the darted parts of the second overwrap ply with one or more filler plies; and h) placing a cap ply in the shape of the platform adjacent to at least one of the first and second overwrap plies. An airfoil with an integrated platform is also disclosed.

BACKGROUND

Blades and vanes in a gas turbine engine typically require platformfeatures to establish continuity of flowpath. In some applications,these platforms are required to be structural, load bearing features asthey transfer aerodynamic loads from the component to the engine staticstructure.

SUMMARY

A method of forming an airfoil with an integrated platform includes: a)providing an airfoil core; b) wrapping a first overwrap ply around theairfoil core; c) darting a first end of the first overwrap ply to allowthe overwrap ply to extend at an angle to the airfoil core to form afirst platform; d) filling the darted parts of the first overwrap plywith one or more filler plies; e) wrapping a second overwrap ply aroundthe first overwrap ply; f) darting a first end of the second overwrapply to allow the second overwrap ply to extend adjacent to the firstoverwrap ply to form the first platform; g) filling the darted parts ofthe second overwrap ply with one or more filler plies; and h) placing acap ply in the shape of the platform adjacent to at least one of thefirst and second overwrap plies.

An airfoil with an integrated platform includes an airfoil core with aleading edge and a trailing edge; a plurality of overwrap pliesextending along the exterior of the airfoil core and extending at anangle to the airfoil core to form a first platform on a first end of theairfoil, wherein the overwrap plies are split in the first platform areato form at least one of a v-dart and a slit dart; one or more fillerplies shaped to fit any v-darts in the overwrap plies; and a pluralityof cap plies connecting adjacent to darted overwrap plies in the firstplatform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an airfoil with integrated platforms.

FIG. 1B is a cross-sectional view of FIG. 1A through the airfoil.

FIG. 1C is an exploded view of the airfoil with integrated platforms ofFIG. 1A.

FIG. 1D is a bottom view of an overwrap ply used in the airfoil of FIG.1A.

FIG. 2 is a method of forming the airfoil of FIG. 1A.

DETAILED DESCRIPTION

FIG. 1A is a perspective view of airfoil 10 with integrated platforms12, 14 and FIG. 1B is a cross sectional view of airfoil 10. FIG. 1C isan exploded view of airfoil 10 showing one overwrap ply 26 and two capplies 28 and FIG. 1D is a bottom view of an overwrap ply 26. Airfoil 10includes airfoil body 11, first platform 12 at first end 13, secondplatform 14 at second end 15, hollow core 16, internal plies 18, filler20, leading edge 22, trailing edge 24, overwrap plies 26, cap plies 28,filler plies 30 and darts 32, 34.

In the embodiment shown, airfoil 10 is hollow and core 16 of airfoil 10includes internal plies 18 to form the basic airfoil hollow pressurevessel and filler 20 to fill the portion of airfoil 10 that has a radiussmaller than the fibers of internal plies 18 can form without breakingwhile maintaining the aerodynamic trailing edge shape 24. Filler 20 canbe laminated composite plies stacked vertically, monolithic ceramicinserts, continuous fiber tow oriented in specific directions, choppedcomposite fibers, or other options that can hold the shape of airfoil 10and provide sharp edges desired for aerodynamic properties. Airfoil 10can be used as a static airfoil in various gas turbine engine parts, forexample, the mid-turbine frame.

Overwrap plies 26 and internal plies 18 can be two-dimensional fiberarchitectures. Elongated fibers extend through plies 18, 26 at specifiedorientations and give plies 18 and 26 strength. Plies 18 and 26 can varyin size, shape and fiber orientation. Plies 18 and 26 can comprise awoven fabric or a unidirectional material. The fabric may be a plainweave, five harness stain (5HS) weave, 8 harness satin (8HS) weave, orany other common woven fiber architecture. During lay-up, these fabricsmay be oriented at any desired angle. The plies, whether fabric orunidirectional, may be woven from a variety of fibers, including, butnot limited to, carbon, glass, aramid and ceramic. They may also be usedin a dry, tackified, wet lay-up or prepregged state depending on themanufacturing method chosen. Plies 18 and 26 can vary in shape and size.The design or ply layup of plies 18 and 26 can be controlled to managethe locations of specific materials and to manage the locations of theedges of plies 18, 26 and darts 32, 34. A ply drop is formed at the edgeof each ply 18 or 26. Ply drops can provide initiation sites for damageand cracks. The weakest region for laminated composites is often theinterlaminar region between plies. High interlaminar stress, such asthat caused by operational loads and foreign object strikes, can causeply delamination that compromises the structural integrity of thestructure. The ply drops in airfoil 10 and platforms 12 and 14 formed atthe edges of plies 18 and 26, are staggered and spread apart to preventcrack propagation throughout the rest of the laminate. Cap plies 28 canbe the same material as internal plies 18 or overwrap plies 26 or can bedifferent depending on airfoil 10 requirements.

Airfoil 10 with integrated platforms 12, 14 is formed by wrapping aplurality of overwrap plies 26 over core 16 and forming platforms 12, 14with overwrap plies 26 and ply caps 28. A first overwrap ply 26 iswrapped around core 16. Overwrap ply 26 is then cut, in the case of afabric, or separated in the case of a unidirectional material, to formdarts 32, 34, allowing it to extend at an angle, for example,perpendicularly, from airfoil body 11 at first end 13 and second end 15.Darts can be v-darts 32 or slit darts 34. V-darts 32 are necessary atlocations of convex curvature around the perimeter of the airfoil,forcing a cut or separation of tows to allow overwrap ply 26 to extendat an angle from airfoil body 11. V-darts 32 can then be filled withfiller plies 30 cut to the shape of v-darts 32. Slit darts 34 arerequired at locations of concave curvature around the perimeter of theairfoil, necessitating that material be removed to allow the ply tocover the desired area without overlapping itself. Another overwrap ply26 is then wrapped around first overwrap ply 26 and darted to layadjacent to first overwrap ply 26 on airfoil body 11 and platforms 12and 14. Darts 32, 34 are staggered between adjacent overwrap plies 26 sothat darts 32, 34 do not lay on top of each other, and create weak faultlines in platforms 12, 14. Airfoil 10 can be made of a plurality ofoverwrap plies 26, for example ten, intermixed with cap plies 28 inplatforms 12, 14.

Cap plies 28 are cut in the shape of platforms 12, 14 to sit adjacent toone or more overwrap plies 26 in platforms 12, 14 to provide acontinuous reinforcement layer in platforms 12, 14. Cap plies 28 can beplaced, for example, between every two or three overwrap plies 26. Capplies 28 can also be placed on the gas flow path side of airfoil 10 togive a smooth air flow surface.

Darts 32, 34 allow overwrap plies 26 to lay flat and not wrinkle orbunch when extending perpendicularly from airfoil body 11. Filler plies30 are inserted to fill in v-darts 32, and cap plies 28 are used tofurther reinforce platforms 12, 14.

FIG. 2 shows method 40 of forming airfoil 10 of FIG. 1A. Method 40includes the steps of providing an airfoil core (step 42), providing acap ply for each end of the airfoil (step 44), wrapping a first overwrapply around the airfoil core (step 46), cutting or separating the ends ofthe first overwrap ply to form darts which allow the ply to extend at anangle to the airfoil core at first and second ends (step 48), cuttingfiller plies to match v-darts (step 50), inserting the cut filler pliesinto the v-darts (step 52), wrapping a second overwrap ply around thefirst overwrap ply (step 54), cutting or separating the ends of thesecond overwrap ply to form darts which allow the ply to extend adjacentto the first overwrap ply at the platforms (step 56), cutting fillerplies to match the v-darts in the second overwrap ply (step 60),inserting cap plies adjacent to second overwrap ply on first end andsecond end (step 62), connecting additional plies (step 64), andperforming additional finishing operations (step 66).

Providing a hollow airfoil core 16 (step 42) can involve wrapping pliesaround an existing core tool or obtaining a core by some other means.Airfoil core 16 can vary in shape, size and properties, but generallymust form at least a portion of airfoil for overwrap plies 26 to connectaround.

Providing a cap ply for each end of the airfoil (step 44) involvesobtaining two cap plies 28, one in the shape of first platform 12 andone in the shape of second platform 14. These will act as the airflowsurface plies for platforms 12, 14, giving a smooth airflow surface forgreater aerodynamic properties. Cap plies can be made or cut from thesame material as overwrap plies, or can be different materials dependingon airfoil 10 requirements.

Wrapping a first overwrap ply 26 around airfoil core (step 46) caninvolve using a wet lay-up, a prepregged material or a tackifier onoverwrap ply 26 to allow it to stick to the core when wrapping. Thetackifier is compatible with the matrix material used in compositeairfoil 10.

Cutting or separating the ends of first overwrap ply 26 to form darts32, 34, allowing ply to extend at an angle to first and second ends 13,15 adjacent to cap plies 28 (step 48) can be done using any cutting toolthat works with the material of overwrap ply 26. The large radius ofcurvature of airfoil 10 produces wrinkling of the fabric as it isextended at an angle to airfoil body 11 to form platforms 12, 14. Inareas where there is too much fabric, slit darts 34 are cut to removefabric from overwrap ply 26. In areas where there is too little fabric,v-darts 32 are cut. Filler plies 30 are then cut to match the shapes ofv-darts 32 (step 50) and inserted into v-darts 32 to form a flat surfaceon platforms 12, 14 (step 52).

Another overwrap ply 26 is then wrapped around first overwrap ply (step54), the ends of the second overwrap ply are cut or separated (in thesame manner as first overwrap ply 26) to form darts allowing the secondoverwrap ply to extend adjacent to the first overwrap ply at platforms(step 56). Darts 32, 34 between adjacent overwrap plies 26 are staggeredto avoid weak fault lines, which could lead to weaker overall platform12, 14. Filler plies 30 are then cut to match v-darts in second overwrapply (step 60), as discussed in relation to first overwrap ply 26.

Inserting a cap ply 28 adjacent to the second overwrap ply on first end13 and second end 15 (step 62) gives platforms 12, 14 a layer ofcontinuous fabric reinforcement. This increases overall strength ofplatforms 12, 14.

Additional plies 18, 26, 28 can be connected (step 64) to form airfoil10 in the same manner as in steps 46 through 62. These steps can beperformed any number of times, or may be performed in any order,depending on the desired requirements for airfoil 10. One example couldinclude an airfoil 10 with five internal pressure vessel plies 18, fiveoverwrap plies 26 and cap plies 28 between every two platform plies 18,26. The outer edges of each side of platforms 12, 14 can be covered withcap plies 28 to provide a smooth, continuous outer surface. Alternativeembodiments could use cap plies 28 between every overwrap ply 26,between every three overwrap plies 26 or not at all.

Performing additional finishing operations (step 66) can include curingairfoil 10, machining airfoil 10 and/or performing controlled hightemperature cycles. To cure airfoil 10 with integral platforms 12, 14, aResin Transfer Molding (RTM) process may be used in which internal plies18, overwrap plies 26, cap plies 28 and filler 20 are placed in a mold,injected with resin and cured. Example resins include but are notlimited to epoxy resins and epoxy resins containing an additive, such asrubber. Alternatively, airfoil plies 18, 26, 28 can be pre-impregnatedcomposites, (i.e. “prepregs”) such that resin is not directly added tothe mold. In a ceramic matrix composite airfoil 10, a pre-ceramicpolymer is used as that matrix material. Once airfoil 10 is cured, itcan be put through high temperature cycles in a controlled environmentthat convert the pre-ceramic polymer into a ceramic. This conversioncauses the volume to change, resulting in a porous material. The part isthen put in another bath of the matrix to fill any crack or voids causedby the change of volume, followed by another controlled high temperaturecycle. This can be repeated a number of times until airfoil 10 reachesthe desired density. Machining can be done at various steps as well.

Method 40 allows for the forming of airfoil 10 with integral platforms12, thereby providing an airfoil with increased strength and stabilityfor handling and transferring loads. Darts 32, 34 allow for extendingplies to form platforms 12, 14 integrally and preventing wrinkling ofthe fabric as plies are extended perpendicularly to airfoil body 11. Capplies 28 provide a continuous surface to reinforce platforms 12, 14 andoverall airfoil 10 and can provide a smooth surface for increasedaerodynamic performance.

While airfoil 10 core 16 is shown as a hollow airfoil with internalplies 18 and filler 20, core 16 can be made of other materials, such asmetal and/or can be solid depending on system requirements. While FIGS.1A-1D show a static airfoil with two platforms, the airfoil could alsohave only one platform and could be a rotating airfoil or it could havetwo platforms and multiple airfoils. Although airfoil platforms 12, 14are shown as being made by extending overwrap plies 26 (and using capplies 28), inner plies (if used in airfoil construction) can also beextended and darted in the same manner as overwrap plies 26 to formplatforms 12, 14. While internal plies have been discussed to beconstructed from individually wrapped plies with staggered seams,internal plies 18 can be constructed by continuously wrapping internalplies around core 16 as many times as needed, reducing the number ofoverall seams.

A method of forming an airfoil with an integrated platform includes: a)providing an airfoil core; b) wrapping a first overwrap ply around theairfoil core; c) darting a first end of the first overwrap ply to allowthe overwrap ply to extend at an angle to the airfoil core to form afirst platform; d) filling the darted parts of the first overwrap plywith one or more filler plies; e) wrapping a second overwrap ply aroundthe first overwrap ply; f) darting a first end of the second overwrapply to allow the second overwrap ply to extend adjacent to the firstoverwrap ply to form the first platform; g) filling the darted parts ofthe second overwrap ply with one or more filler plies; and h) placing acap ply in the shape of the platform adjacent to at least one of thefirst and second overwrap plies.

Additional and/or alternative embodiments include: placing a cap plyadjacent to the first overwrap ply to form the surface of the platformflow path; repeating steps (b)-(h) at least one time; darting a secondend of the first overwrap ply to allow it to extend at an angle to theairfoil core to form a second platform; filling the darted parts of thesecond overwrap ply with one or more filler plies; step (f) furthercomprising darting a second end of the second overwrap ply to allow itto extend at an angle to the airfoil core adjacent to the first ply toform the second platform; step (g) further comprising filling the dartedportions of the second end of the second overwrap ply with one or morefiller plies; step (h) further comprising placing a second cap ply inthe shape of the platform adjacent to the second overwrap ply formingthe second platform; repeating steps (b)-(h) at least one time; step (a)further comprising wrapping internal plies around the airfoil core; andinserting filler material; and/or extending the internal plies to form apart of the first platform.

An airfoil with an integrated platform includes an airfoil core with aleading edge and a trailing edge; a plurality of overwrap pliesextending along the exterior of the airfoil core and extending at anangle to the airfoil core to form a first platform on a first end of theairfoil, wherein the overwrap plies are cut in the first platform areato form at least one of a v-dart and a slice dart; one or more fillerplies shaped to fit any v-darts in the overwrap plies; and a pluralityof cap plies connecting adjacent to darted overwrap plies in the firstplatform.

Additional and/or alternative embodiments include a second platformformed by darting the overwrap plies on a second end of the airfoil toinclude at least one of v-darts and slice darts; the second platformfurther comprising one or more filler plies to fit into the areas of thev-darts in the second platform; and one or more cap plies to fitadjacent to darted overwrap plies in the second platform; locallystaggering the darts; at least one of the cap plies being locatedbetween every two darted plies; a cap ply forming the flow path surfaceon the first platform; and/or the airfoil core being hollow.

A method of forming an airfoil includes (a) providing an airfoil core;(b) wrapping internal plies around the airfoil core; (c) insertingfiller material; (d) wrapping a first overwrap ply around the internalplies and filler material; (e) darting the first overwrap ply in one ormore places at a first end to allow the first overwrap ply to extend atan angle to the airfoil core to form a first platform; (f) inserting oneor more first filler plies in any darts formed from darting the firstoverwrap ply; (g) covering the first overwrap ply with a second overwrapply; (h) darting the second overwrap ply in one or more places at thefirst end to allow it to extend at an angle to the airfoil core adjacentto the first overwrap ply on the first platform; (i) inserting one ormore second filler plies into any darts formed from darting the secondoverwrap ply; and (j) attaching a first cover ply in the shape of thefirst platform adjacent to one or more of the first and second plies.

Additional and/or alternative embodiments include performing steps(d)-(j) a plurality of times; extending internal plies to the firstplatform; forming a pressure vessel from the internal plies and forminga sharp trailing edge from filler; (i) darting the overwrap ply in oneor more places at a second end to allow it to extend at an angle to theairfoil core to form a second platform; (j) inserting one or more thirdfiller plies in any darts formed from darting the first overwrap ply atthe second end; (k) darting the second overwrap ply in one or moreplaces at the second end to allow it to extend perpendicular to theairfoil core adjacent to the first overwrap ply on the second platform;(1) inserting one or more fourth filler plies into any darts formed fromdarting the second overwrap ply at the second end; and (m) attaching asecond cover ply in the shape of the second platform adjacent to one ormore of the first and second plies; and/or performing steps (b)-(m) aplurality of times.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A method of forming an airfoil with an integrated platform, themethod comprising: a) providing an airfoil core; b) wrapping a firstoverwrap ply around the airfoil core; c) darting a first end of thefirst overwrap ply to allow the overwrap ply to extend at an angle tothe airfoil core to form a first platform; d) filling the darted partsof the first overwrap ply with one or more filler plies; e) wrapping asecond overwrap ply around the first overwrap ply; f) darting a firstend of the second overwrap ply to allow the second overwrap ply toextend adjacent to the first overwrap ply to form the first platform; g)filling the darted parts of the second overwrap ply with one or morefiller plies; and h) placing a cap ply in the shape of the platformadjacent to at least one of the first and second overwrap plies.
 2. Themethod of claim 1, and further comprising: placing a cap ply adjacent tothe first overwrap ply to form the surface of the platform flow path. 3.The method of claim 1, wherein steps (b)-(h) are repeated at least onetime.
 4. The method of claim 1, wherein step (c) further comprises:darting a second end of the first overwrap ply to allow it to extend atan angle to the airfoil core to form a second platform.
 5. The method ofclaim 4, wherein step (d) further comprises: filling the darted parts ofthe second overwrap ply with one or more filler plies.
 6. The method ofclaim 5, wherein step (f) further comprises: darting a second end of thesecond overwrap ply to allow it to extend at an angle to the airfoilcore adjacent to the first ply to form the second platform.
 7. Themethod of claim 6, wherein step (g) further comprises: filling thedarted portions of the second end of the second overwrap ply with one ormore filler plies.
 8. The method of claim 7, wherein step (h) furthercomprises: placing a second cap ply in the shape of the platformadjacent to the second overwrap ply forming the second platform.
 9. Themethod of claim 8, wherein steps (b)-(h) are repeated at least one time.10. The method of claim 1, where step (a) further comprises: wrappinginternal plies around the airfoil core; and inserting filler material.11. The method of claim 10, wherein the internal plies are extended toform a part of the first platform.
 12. An airfoil with an integratedplatform comprising: an airfoil core with a leading edge and a trailingedge; a plurality of overwrap plies extending along the exterior of theairfoil core and extending at an angle to the airfoil body to form afirst platform on a first end of the airfoil, wherein the overwrap pliesare split in the first platform area to form at least one of a v-dartand a slit dart; one or more filler plies shaped to fit any v-darts inthe overwrap plies; and a plurality of cap plies connecting adjacent todarted overwrap plies in the first platform.
 13. The airfoil of claim12, and further comprising: a second platform formed by darting theoverwrap plies on a second end of the airfoil to include at least one ofv-darts and slice darts.
 14. The airfoil of claim 13, wherein the secondplatform further comprises: one or more filler plies to fit into theareas of the v-darts in the second platform; and one or more cap pliesto fit adjacent to darted overwrap plies in the second platform.
 15. Theairfoil of claim 12, wherein the darts are locally staggered.
 16. Theairfoil of claim 12, wherein at least one of the cap plies is locatedbetween every two darted plies.
 17. The airfoil of claim 12, wherein acap ply forms the flow path surface on the first platform.
 18. Theairfoil of claim 12, wherein the airfoil core is a hollow core.
 19. Amethod of forming an airfoil comprising: (a) providing an airfoil core;(b) wrapping internal plies around the airfoil core; (c) insertingfiller material; (d) wrapping a first overwrap ply around the internalplies and filler material; (e) darting the first overwrap ply in one ormore places at a first end to allow the first overwrap ply to extend atan angle to the airfoil core to form a first platform; (f) inserting oneor more first filler plies in any darts formed from darting the firstoverwrap ply; (g) covering the first overwrap ply with a second overwrapply; (h) darting the second overwrap ply in one or more places at thefirst end to allow it to extend at an angle to the airfoil core adjacentto the first overwrap ply on the first platform; (i) inserting one ormore second filler plies into any darts formed from darting the secondoverwrap ply; and (j) attaching a first cover ply in the shape of thefirst platform adjacent to one or more of the first and second plies.20. The method of claim 19, wherein steps (d)-(j) are performed aplurality of times.
 21. The method of claim 19, wherein the internalplies extend to the first platform.
 22. The method of claim 21, whereinthe internal plies form a pressure vessel and the filler forms a sharptrailing edge.
 23. The method of claim 19, and further comprising: (i)darting the overwrap ply in one or more places at a second end to allowit to extend at an angle to the airfoil core to form a second platform;(j) inserting one or more third filler plies in any darts formed fromdarting the first overwrap ply at the second end; (k) darting the secondoverwrap ply in one or more places at the second end to allow it toextend perpendicular to the airfoil core adjacent to the first overwrapply on the second platform; (l) inserting one or more fourth fillerplies into any darts formed from darting the second overwrap ply at thesecond end; and (m) attaching a second cover ply in the shape of thesecond platform adjacent to one or more of the first and second plies.24. The method of claim 23, wherein steps (b)-(m) are performed aplurality of times.